The utilization of neurostimulation implant devices is ever-increasing. Such devices typically utilize a plurality of implanted electrodes that are selectively activated to affect a desired neuro-response, including sound sensation, pain/tremor management, and urinary/anal incontinence. By way of primary interest, auditory neurostimulation implant devices include auditory brainstem implant (ABI) and cochlear implant (CI) devices.
In the case of typical CI devices, an active electrode array may be inserted into the cochlea of a patient, e.g. typically into the scala tympani so as to access and follow the spiral curvature of the cochlea. The array electrodes are selectively driven to stimulate the patient's auditory nerve endings to generate sound sensation. In this regard, a CI electrode array works by utilizing the tonotopic organization, or frequency-to-location mapping, of the basilar membrane of the inner ear. In a normal ear, sound vibrations in the air are transduced to physical vibrations of the basilar membrane inside the cochlea. High frequency sounds do not travel very far along the membrane, while lower frequency sounds pass further along. The movement of hair cells, located along the basilar membrane, creates an electrical disturbance, or potential, that can be picked up by auditory nerve endings that generate electrical action pulses that travel along the auditory nerve to the brainstem. In turn, the brain is able to interpret the nerve activity to determine which area of the basilar membrane is resonating, and therefore what sound frequency is being sensed. By directing which electrodes of a CI electrode array are activated, cochlear implants can selectively stimulate different parts of the cochlea and thereby convey different acoustic frequencies corresponding with a given audio input signal.
With typical ABI systems a plurality of active electrodes may be implanted at a location that bypasses the cochlea. More particularly, an array of electrodes may be implanted at the cochlea nucleus, or auditory cortex, at the base of the brain to directly stimulate the brainstem of a patient. Again, the electrode array may be driven in relation to the tonotopic organization of a recipient's auditory cortex to obtain the desired sound sensation.
As may be appreciated, in the case of either ABI electrodes or CI electrodes, audio signals (e.g. from a microphone) may be processed, (e.g. by a speech processor), and utilized to generate stimulation signals utilized to selectively drive the active electrodes for stimulated sound sensation. Further, in both implant approaches, one or more reference electrodes may be interconnected to the source or generator of the active electric stimulation signals. In this regard, it is desirable to provide a consistent, or stable, reference signal to realize optimal signal generation.